The invention lies in the automotive field. Specifically, the invention relates to a brake system for a motor vehicle with rear end collision impact mitigation.
Motor vehicles such as automobiles have a brake system which, upon actuation, brakes all wheels. Such brake systems are hydraulic pump systems in most modem vehicles. When a brake pedal is actuated by the driver, an actuator shaft translates the brake pedal pressure onto a piston/cylinder arrangement and the pressure in the cylinder is increased. The cylinder is generally referred to as the master cylinder. The master cylinder is bound into a closed loop hydraulic pressure system with a separate brake cylinder assigned to each wheel. The force (pressure) at the master cylinder causes a displacement at the individual wheel brake cylinders and the brake pedal force, i.e. its displacement, is translated to a brake pad or caliper displacement at the wheel. The hydraulic fluid is substantially incompressible.
These most widely prevalent brake systems have recently been replaced or augmented by electrical systems, so-called brake-by-wire systems. In the electrical brake system, the brake pedal force is not mechanically transmitted to the wheel brakes by way of the hydraulic fluid. Instead, the pedal displacement and force is measured and electronically processed. Individual electric actuators are thereupon triggered at the individual wheels so as to brake the wheels.
The electrical brake system is particularly suitable in the context of wheel slip regulators, such as anti-lock brake systems. In the hydraulic brake system, of course, the anti-lock brake system is quite complicated and expensive in that a full set of additional actuators must be provided so as to override or compensate against the force of the hydraulic wheel cylinder at each wheel. Furthermore, the purely mechanical hydraulic system does not in and of itself provide any measured force values which could be used in the processing of the anti-lock action of the additional inline actuators. In contrast, in the brake-by-wire system, the anti-lock actuation process can be fully integrated in the electronic processing and electrical triggering of the wheel brakes.
A well-developed anti-lock brake system is described, for instance, in U.S. Pat. No. 5,312,170 to Erban et al. and the various references described in the patent. As in all related ABS systems, the anti-lock process is described in two phases, namely the brake regulation phase in which the brake is actuated until a setpoint slip value is reached and a brake pressure control if the pertinent wheel is unstable in operation.
A method and a corresponding configuration for determining a frictional value between the tire and the road surface is described in U.S. Pat. No. 5,513,907 to Kiencke et al. There, the speed of the vehicle, the brake pressure at each wheel, and the angular acceleration of the wheel are introduced into the calculation which determines the actual coefficient of friction between the tire and the road.
Despite the substantial advances in automotive technology in regards to brake systems, impact reduction measures (bending body cages, forced restraint systems, air bags, etc.), and early impact warning sensors, the automobile is still less than acceptably safe. One specific source of personal injury and property damage are rear impact collisions. The primary damage done by rear impact collisions is the body damage to the rear of the forward vehicle and to the front end of the rear vehicle. Slight impact collisions are damped and fully compensated by front and rear shock-absorbing bumpers.
Stronger impact forces caused by collisions at relative speeds of, say, more than 20 kmh (≈12 mph) also have a tendency to injure the persons in the vehicles. Due to the substantial advances in driver and passenger restraint systems (for instance tightening seat belts, airbags), which largely concentrate on front and side impact, the persons in the rear vehicle are, or should be, well protected. The persons in the forward vehicle, on the other hand, are very suddenly jolted backwards (in fact, of course, the car accelerates forward very quickly and the persons and other relatively loose objects observe Newton""s first law instead of lunging forward together with the forward vehicle) upon the impact. The most prevalent injury which results from such rear impact collisions is known as whiplash. Bodily injury, of course, is typically rated with a higher priority than mechanical damage to the vehicle body. In monetary terms, medical bills for full treatment of whiplash injuries are very often substantially higher than the repair costs for body damage done to the vehicles.
In addition to the damage done to the two vehicles that are directly involved, it often happens that the forward vehicle is propelled forward by the impact force and thereby collides with yet another vehicle. Domino-effect chain reactions with multiple injuries are quite possible even at relatively small rear impact speed.
The resulting whiplash, and the possible involvement of further vehicles, could be substantially reduced, were it not for a little observed phenomenon. Most rear end collisions occur when the forward vehicle is either at a standstill or is being decelerated. In either case, the driver""s foot applies a braking force by pushing the brake pedal forward. When the impact from the rear end collision accelerates the vehicle forward, the driver""s foot is lifted from the brake pedal (again, this is Newton""s first law) and the brakes are released. As a result, the resistance of the forward vehicle against the sudden acceleration is reduced to a minimum. As will be seen from the following calculations, the continued, or even increased, application of the vehicle brakes can indeed have a substantial mitigating effect on the resulting damage.
It is accordingly an object of the invention to provide a motor vehicle brake system with rear impact mitigation, which overcomes the above-mentioned disadvantages of the prior art devices and methods of this general type and which with the foregoing and other objects in view there is provided, in accordance with the invention, a brake system for a motor vehicle with a front end, a rear end, and a plurality of wheels, comprising:
a sensor disposed in a motor vehicle for sensing a rear impact collision and outputting an impact signal;
a brake processor connected to the sensor to receive the impact signal from the sensor indicating a rear impact collision;
the brake processor applying a braking force to at least one wheel of the motor vehicle upon determining that a rear impact collision has occurred.
In accordance with an added feature of the invention, the sensor, or one of a plurality of sensors, is an acceleration sensor. In a preferred embodiment, the acceleration sensor has four sensitivity axes for sensing forward acceleration, rearward acceleration, and two mutually opposite lateral accelerations, respectively.
In a most inexpensive implementation of the brake system of the invention, the system makes used of the acceleration sensor that already forms a part of the passenger protection system of the motor vehicle. The standard passenger protection system includes sensors, processors, and trigger algorithms for air bags and for belt tensioners (as well as the ABS or traction control implementation for the brake system). In that case, only the triggering program of the protection system must be adapted to trigger a braking force on a corresponding rear impact.
In accordance with an additional feature of the invention, the above-noted sensor is included in a plurality of sensors that are strategically disposed throughout the motor vehicle, including at positions at the rear end of the motor vehicle.
In accordance with another feature of the invention, the processor is programmed to:
continuously monitor a travel speed of the vehicle and measure a braking force being applied during an operation of the vehicle;
define a class of impacts requiring a brake intervention in dependence on the travel speed and on whether the vehicle brake was applied at an outset of the rear impact collision;
block the brakes with a maximum braking force if the vehicle was at a standstill and the vehicle brake was applied at an outset of the rear impact collision; and
apply a braking force equivalent to the braking force last measured prior to a rear impact immediately upon an outset of the rear impact collision.
With the above and other objects in view there is also provided, in accordance with the invention, a passenger protection method in a motor vehicle. The method comprises the following steps:
sensing a sudden impact at a rear end of a motor vehicle and outputting an impact signal representing a rear impact collision;
receiving and processing the impact signal to determine whether the rear impact is one of a class of impacts requiring brake intervention; and
if the rear impact belongs to the class of impacts requiring brake intervention, applying a braking force to at least one wheel of the motor vehicle.
In accordance with a preferred mode of the invention, the travel speed of the vehicle is constantly monitored and recorded and the system also monitors constantly whether the vehicle brakes are being applied. The class of impacts requiring brake intervention are then defined in dependence on the travel speed and on whether the vehicle brake was applied at an outset of the rear impact collision.
In accordance with a further feature of the invention, if the vehicle was at a standstill and a vehicle brake was applied at an outset of the rear impact collision, the applying step comprises blocking the brakes with a maximum braking force.
In accordance with a concomitant feature of the invention, the travel speed of the vehicle is continuously monitored and the braking force being applied during an operation of the vehicle is continuously measured. The above-noted applying step then comprises applying the braking force last measured prior to a rear impact immediately upon an outset of the rear impact collision.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied is in a motor vehicle brake system and method, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.